1. Field of the Invention
The present invention relates generally to hydraulic devices and, more particularly, to hydraulic cylinder devices capable of internal hydraulic intensification for power multiplication.
2. The Prior Art
In many applications hydraulic cylinders are required which are capable of producing a quick stroke of little power or force and a subsequent short, slow stroke of relatively greater power. In applications such as manufacturing machines and presses as well as ram and tractive type apparatus used for excavation, hydraulic cylinders with hydraulic intensification are used. Such cylinders are more compact and lighter than single-stage hydraulic cylinders of equal work power.
Hydraulic cylinders with hydraulic intensification which contain two successive pistons and three chambers are known see, for example, British Pat. Nos. 1,600,733 and 1,420,389; U.S. Pat. No. 4,011,724 and German Published Application No. 31 19 307 Al. With such a construction for a hydraulic cylinder, a dividing wall is required between the pistons and the pistons move in the same direction during a work cycle, e.g., during a clamping operation. As a consequence, the length of the cylinder must be increased up to twice the thickness of the dividing wall. Furthermore, if the primary piston encounters no resistance during its movement, the intensification cycle will be initiated when the piston contacts the cover of the cylinder. Consequently, the cylinder cover must be designed to have sufficient strength to avoid breakage during intensification, which contributes significantly to the overall size and weight of the hydraulic cylinder.